GIS Information

Colours on Maps

The art of mapping from GIS is Cartography. The use of symbols, colours and layout to make a map more easily understandable is often left out of mapping with GIS. It is a waste when the extensive time and effort that went into the collection, analysis and display of the information results in a map that is hard to read and understand. Each map should be clear in its message and speak to the intended audience in a way that they can understand. Too much information can be confusing, too little and you can’t find the information you need.
Colour is a key element in conveying the message on a map, and one of the best sites to get help is at ColorBrewer.
 

(http://colorbrewer2.org/)

South African Coordinate Systems

Official since 1st January 1999: World Geodetic System 1984 ellipsoid, with the official Datum: Hartebeesthoek94 Originally: Modified Clarke 1880 ellipsoid, with the Cape Datum Both of the above are Geographic (Spherical) Coordinate Systems, suitable for use when you are modelling the real world, but to create a flat map you need to use a Projected Coordinate System. In South Africa that is the South Oriented Transverse Mercator also known as Gauss-Krüger or Gauss conformal projection. The projection is conformal meaning that shape and angle are preserved at the expense of distance and area.

For more information visit:
http://www.gpswaypoints.co.za/FAQ_world_geodetic_system_1984.htm

In South Africa the scale factor always has a value of one. It is standard practice to use each odd numbered parallel (15, 17, 19, 21, 23, 25 (Port Elizabeth), 27 (East London), 29, 31 and 33) as a central meridian. It is also standard practice not to apply false eastings and northings. Download the NMBM (Port Elizabeth) and SAEastLondon (East London) ESRI projection files from the Downloads Section – choose “Modify” in ArcGIS to see how to create your own by setting the Meridian (parallel) suitable for your area.

Using ArcGIS you should store your datasets in either WGS84 or GCS Hartebeesthoek94 and then set the map Data Frame Properties / Coordinate System to the Projected Coordinate System.

To convert between WGS84 and Hartebeesthoek94 use the Transformation:
Hartebeesthoek94_to_WGS_1984 (it works in either direction).
To convert between Hartebeesthoek94 and Cape use the Transformation:
Cape_To_Hartebeesthoek94 (it works in either direction).



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